The blood complement (C) plays an important role in host defense to foreign substances. Individuals that are deficient in certain C components often suffer recurrent and sometimes fatal infections. Activation of the C system results in the production of the anaphylatoxins, C3a and C5a. These fragments are biologically active cleavage products of the larger C proteins C3 and C5, respectively. C5a is a short (74 residues in human) glycoprotein that is generated by enzymatic cleavage of C5.
C5a is recognized as a principal mediator of local and systemic inflammatory responses because of its ability to activate and recruit neutrophils, induce spasmogenesis, increase vascular permeability and stimulate the release of secondary inflammatory mediators from a variety of cell types (e.g., leukocytes and macrophages). C5a also appears to play a role in the modulation of immune response because of its ability to induce, directly or indirectly, the synthesis and release of the cytokines interleukin-1 (IL-1), interleuken-6 (IL-6), interleukin-8 (IL-8), and tumor necrosis factor-α (TNF-α) from human monocytes. These inflammatory and immunomodulatory activities are believed to be expressed via a transmembrane, G-protein-mediated signal transduction mechanism when the C5a ligand interacts with its receptor(s) expressed on the surface of certain circulating and tissue cell types.
The proinflammatory activities of C5a may be classified into two broad categories. The first category of activity is generally associated with the release of histamines and other secondary mediators (e.g., vasoconstrictor and vasodilator eicosanoids). These activities of C5a affect many systems, and are associated with the phenomena of spasmogenesis and certain cell aggregatory activities (e.g., platelet aggregation). The second category of activity involves recruitment and activation of neutrophils and subsequent effects of such neutrophil accumulation and activation, such as increased vascular permeability, release of cytokines and other pro-inflammatory responses. The in vivo pharmacology of these two broad classes of C5a activities is described briefly by Drapeau et al. (1993), Biochem. Pharmacol., 45: 1289-1299. The regulation of neutrophils and other leukocytes by C5a has been reviewed by Hugh & Morgan (1984), Chapter 4 in Regulation of Leukocyte Function, R. Snyderman, ed., Plenum Publishing Corp., pp. 109-153.
Because of its proinflammatory activity, C5a has been implicated as a pathogenic factor in the expression of certain inflammatory disorders, such as rheumatoid arthritis, adult respiratory distress syndrome, gingivitis, and the tissue damage associated with atherosclerosis and myocardial infarction. Consequently, considerable research efforts have been expended in developing specific C5a antagonists for use as anti-inflammatory agents in the treatment of these diseases.
C-terminal C5a peptide analogs have been produced and studied for the purpose of developing C5a agonists and antagonists. For example, Ember et al. (Ember et al. (1992), J. Immunol., 148: 3165-3173) characterized the biological activities of 22 synthetic C-terminal C5a analogs. The analogs were reported to be full agonists of natural C5a, having in vitro activities characteristic of naturally occurring C5a, including the ability to stimulate ileal contraction (i.e., spasmogenesis) platelet aggregatory activation and neutrophil polarization and chemotaxis. However, the potencies of even the most effective of these analogs was on the order of only 0.01-0.25% that of the natural factor. This level of potency could be obtained with analogs as short as decapeptides, as compared with longer C-terminal peptides that had previously been studied as potential agonists. Morgan et al. (1992), J. Immunol., 148: 3937-3942, reported that certain of the peptide analogs disclosed by Ember et al. stimulated synthesis of interleukin-6 in human peripheral blood mononuclear cells. Again, however, potency of these peptide analogs was on the order of 0.01-0.1% of either natural or recombinant C5a. Drapeau et al. (supra) reported on the pharmacology, metabolism and in vivo cardiovascular and hematologic effects of synthetic C-terminal C5a peptide analogs based on either human or porcine amino acid sequences. These analogs were also found to be agonists of natural C5a, but were disclosed as being at least 1,000-fold less potent than recombinant C5a as measured by competition for C5a binding sites.
C-terminal C5a peptide analogs have also been studied with respect to the ability of such analogs to bind to C5a receptors. Kawai et al. (1992), J. Med. Chem., 35: 220-223, reported on relationships between the hydrophobicity and chirality of residues 70-73 of C-terminal octapeptide analogs and the ability of such analogs to bind to C5a receptors. However, biological responses elicited by these octapeptide analogs was not reported. In other studies, it has been determined that substitution of phenylalanine or tryptophan in positions between 65 and 69 of the human C5a C-terminus could enhance or decrease potency, depending on whether the substitution was made at position 67 or at position 66 (Or et al. (1992) J. Med. Chem. 35: 402-406; Mollison et al. (1991) Agents Actions Suppl. 35:17-21; Siciliano et al. (1994) Proc. Natl. Acad. Sci USA 91:1214-1218). In other studies, these observations were corroborated with reports that substitution of phenylalanine for histidine at position 67 substantially increased the potency of a number of C-terminal peptide analogs of human C5a (Mollison et al. (1991), Agents and Actions, Suppl. 35: 17-21; Or et al. J. Med. Chem., (1992), 35: 402-406; and Kohl et al. (1993), Eur. J. Immunol., 23: 646-652). These reports did not address any differences among the various peptide analogs with respect to their effectiveness for eliciting specific biological responses associated with C5a.
U.S. Pat. No. 5,696,230, which is incorporated by reference in its entirety, describes a conformational characterization of C-terminal peptide analogs of human C5a. U.S. Pat. No. 6,821,517, also incorporated by reference in its entirety, describes compositions and methods for delivering specific antigens to antigen-presenting cells (APCs). Several research articles have published that similarly describe the use of a C-terminal analog of C5a conjugated to a specific antigen (Tempero et al. (1996) J. Immunol. 158:1377-1382; Buchner et al. (1996) J. Immunol. 158:1670-1680; Ulrich et al. (2000) J. Immunol. 164:5492-5498; Sanderson et al. (2003) Int. Immunopharmacol. 3:137-146; Floreani et al. (2007) Cell Cycle 6:2835-2839; Hegde et al. (2008) Int. Immunopharmacol. 8:819-827; Duryee et al. (2009) Vaccine 27:2981-2988; Morgan et al., Vaccine, 28(2): 463-469 (2009); Morgan et al. (2010) Vaccine 28:8275-8279).
To date, the use of oligopeptide C-terminal analogs of C5a, that are not conjugated to a specific antigen, have not been shown to demonstrate therapeutic properties for treating infections and diseases.
Thus, a need exists to develop therapeutic molecules useful for the treatment of infections and diseases, including infections caused by antibiotic resistant bacteria and bacterial burdens due to biofilms.